PIC16F877ATISLASHML datasheet(40/234 Pages) MICROCHIP

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PIC16F87XA

DS39582B-page 38

 2003 Microchip Technology Inc.

An example of the complete four-word write sequence

is shown in Example 3-4. The initial address is loaded

into the EEADRH:EEADR register pair; the four words

of data are loaded using indirect addressing.

EXAMPLE 3-4:

WRITING TO FLASH PROGRAM MEMORY

; This write routine assumes the following:

;

; 1. A valid starting address (the least significant bits = ‘00’)is loaded in ADDRH:ADDRL

; 2. The 8 bytes of data are loaded, starting at the address in DATADDR

; 3. ADDRH, ADDRL and DATADDR are all located in shared data memory 0x70 - 0x7f

;

BSF

STATUS,RP1

;

BCF

STATUS,RP0

; Bank 2

MOVF

ADDRH,W

; Load initial address

MOVWF

EEADRH

;

MOVF

ADDRL,W

;

MOVWF

EEADR

;

MOVF

DATAADDR,W

; Load initial data address

MOVWF

FSR

;

LOOP

MOVF

INDF,W

; Load first data byte into lower

MOVWF

EEDATA

;

INCF

FSR,F

; Next byte

MOVF

INDF,W

; Load second data byte into upper

MOVWF

EEDATH

;

INCF

FSR,F

;

BSF

STATUS,RP0

; Bank 3

BSF

EECON1,EEPGD

; Point to program memory

BSF

EECON1,WREN

; Enable writes

BCF

INTCON,GIE

; Disable interrupts (if using)

MOVLW

55h

; Start of required write sequence:

MOVWF

EECON2

; Write 55h

MOVLW

AAh

;

MOVWF

EECON2

; Write AAh

BSF

EECON1,WR

; Set WR bit to begin write

NOP

; Any instructions here are ignored as processor

; halts to begin write sequence

NOP

; processor will stop here and wait for write complete

; after write processor continues with 3rd instruction

BCF

EECON1,WREN

; Disable writes

BSF

INTCON,GIE

; Enable interrupts (if using)

BCF

STATUS,RP0

; Bank 2

INCF

EEADR,F

; Increment address

MOVF

EEADR,W

; Check if lower two bits of address are ‘00’

ANDLW

0x03

; Indicates when four words have been programmed

XORLW

0x03

;

BTFSC

STATUS,Z

; Exit if more than four words,

GOTO

LOOP

; Continue if less than four words

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